Envelopes are often one of the most diffcult media to have printed on automatic printers such as ink jet printers. The reason is that they are usually irregular in shape, and in any event have multiple-plys non-uniformly distributed. Thus, if the envelopes are not properly held, they tend to become skewed in the printer.
The early approaches to this problem have been to print addresses on peel-off labels, which can be run through printers on standard printer sheets. However, such labels require separate peel-and-stick steps. These render the appearance of being bulk mail, and hence unimportant mail to be discarded. Therefore, there has been a substantial need to provide a way for printing directly onto envelopes that are somehow held in a printer.
Holders have been provided for holding individual sheets on a sprocket-fed support that feeds through a printer. Such holders have a pocket that holds a portion that is not to be printed, the pocket being formed by an upper sheet sealed around three edges to a lower sheet. Examples are shown in, e.g. U.S. Pat. No. 4,591,146. In holders of that type, theupper sheet longitudinal edges are less than 15% of the potential depth of the pocket as measured by the longitudinally extending edges of the lower support of the holder, under the media. In other words, very little side edge engagement of the media is provided by the holder. Thus, such pockets are not suitable for holding envelopes, or other materials of non-uniform thickness. For one thing, they do not account for the fact that the non-uniformity of the envelope will cause it to skew as it passes through the printer, unless the envelope is properly held at the side edges that parallel the sprocket-hole edges. As will be shown hereinafter, attempts to prevent skewing by supporting hereinafter, attempts to prevent skewing by supporting the entire side edges of the envelope that parallel the sprocket edges of the support, tend to result in unacceptable binding or jamming of holder plus envelope, in the printer mechanism.